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Webster 1828 Edition

adv.

With pain; painfully; with great pain or distress; as, to be grievously afflicted.

With discontent, ill will or grief.

Calamitously; miserably; greatly; with great uneasiness, distress or grief.

Atrociously; as, to sin or offend grievously.

grievously ‎(comparative more grievously, superlative most grievously)

In a grievous manner, severely.
- 2011 November 21, David Gergen, “Have they gone nuts in Washington?”, in CNN.com:
  That's why this failure of the super committee represents a reckless, irresponsible gamble by our "leaders" in Washington. It's difficult to remember a Congress that has put the nation so much at risk in the service of ideology and to hold onto office. Partisans on both sides are grievously failing the country.

in a grievous manner